People given larger portion sizes will continue to overeat compared with those given smaller servings, even after they have been expressly told of the impact of portion size on consumption, according to new research from the University of New South Wales (UNSW).

The report found that learning how to engage in mindful – rather than mindless – eating also had little impact on those given larger servings.

“If no effective approaches are found, it may be necessary to develop policy-related changes to provide a healthier food environment for people,” said Dr Lenny Vartanian, a senior lecturer in the UNSW School of Psychology and an author of the paper.

Dr Vartanian says that portion sizes in restaurants and the home have risen dramatically since the 1970s, and are thought to have contributed to rising obesity levels.

“Studies have consistently shown that increases in portion sizes for a wide range of foods and beverages result in increased energy intake. And the impact is not affected by factors such as hunger or the taste of the food,” Dr Vartanian said.

The team’s study of 96 women is the first to examine the effectiveness of educating people about this phenomenon. Participants were served either a 350 gram portion of macaroni pasta with tomato sauce for lunch, or a 600 gram portion.

Those in the education group were given a brochure about how external factors, such as mood, advertising, portion size, and social and cultural influences can contribute to overeating, and then asked to write about how these factors had influenced their food intake in the past.